Conveyor belts comprised of transverse rods connected by links disposed along the opposite transverse edges of the belt have been in use for a long period of time. One such prior art belt uses generally U-shaped nestable links with slotted holes that allow the links to slide on the rods. The relative sliding action betwen the links and rods provides lateral flexibility which enables the belt to turn right or left, when such nestable links are used on both sides of the belt. When such a belt proceeds around a lateral curve, the rod ends along the inside concave edge of the belt collapse. The opposite transverse ends of the rods along the outside convex edge of the belt either remain at the same pitch as when the belt travels in a straight line direction, such as disclosed in U.S. Pat. No. 3,225,898 to Roinestad, or expand to a greater pitch in order to allow the belt to proceed around a smaller radius, as disclosed in U.S. Pat. No. 4,078,655 to Roinestad.
The collapsing or diminshing pitch of the belt along the inside edge of a lateral curve cretes several problems. First of all, most ware is charged into a conveying system in a rank and file arrangement, and spacing of the ranks (crosswise rows) can only be controlled by adjusting the relative speeds of the individual feed conveyors. To make certain that the ware does not overlap, it is necessary to take into account the collapsing pitch and to also leave a safety margin in the spacing, both of which result in a drop in efficiency. If the ware being conveyed is soft in nature, the collapsing pitch can result in wrinkling of the ware. Also, if the conveyor is used in a freezing plant, the collapsing pitch can result in contact and freezing together of adjacent ware if sufficient spacing is not used.
U.S. Pat. No. 4,662,509 issued to Kaak on May 5, 1987 addresses the problem of a conveyor belt having a collapsing inner edge in a chain type conveyor belt wherein the ware support carriers are connected directly to a drive chain. The chain conveyor belt in the '509 patent uses triangular carriers consisting of a rod-shaped element and a pulling element. Along the inside edge of the conveyor belt, the rod-shaped element and the pulling element are pivotably connected to the drive chain, and the pitch of the rod-shaped elements is held constant by the connection to the drive chain. The pulling elements slant backward in the direction of travel of the belt and are pivotably connected to one of the rod-shaped elements further rearward along the belt. As the belt proceeds around a curve, the outside, free ends of the rod-shaped elements increase their spacing or pitch with respect to one another.
The conveyor belt disclosed in the '509 patent, however, has certain disadvantages or limitations. The triangular configuration of the ware carriers precludes negotiation about end pulleys or rolls, or operating through a verticle hanging take-up mechanism. The practical width of the ware carriers is limited by the triangular configuration, because the effectiveness of the pulling element diminishes with increasing width. Finally, the overlapping orientation of the pulling and rod-shaped elements gives rise to serious sanitation difficulties. The capability to clean between all elements of a belt is important when the conveyor belt is used in a food handling environment.
It has also been discovered that the use of a link mechanism which keeps the inside rod ends at a constant pitch along the inner concave edge of a belt, both with dual pitch links and with nestable U-shaped outside links is particularly suitable for use in a conveying system wherein the belt travels along a helical path with the belt being arranged in a number of superimposed helically extending tiers. Prior art helical tier systems, such as disclosed in U.S. Pat. Nos. 3,348,659 and 4,078,655 to Gerald C. Roinestad have used conveying belts with a collapsing inner edge. The successive tiers of belt in the '659 and '655 patents are supported by a support frame separate from the belt. The minimum tier height in such a system is equal to the sum of the heights of the separate belt support frame, the ware being conveyed and the belt, resulting in a system with a relatively large vertical extent. U.S. Pat. No. 3,938,651 to Alfred et al. discloses a conveying system for conveying in a helical path wherein the belt is self-supporting along both the inner and outer edges of the belt.
Another aspect of the invention is directed to the construction of the U-shaped links, particularly the construction of the portion connecting the legs of the link. It has been known in the prior art to curve the bearing surface of the connecting portion of U-shaped links. For example, the bearing surface of certain pintel chain links manufacured by the Allied-Locke Industries, Incorporated are curved. However, such prior art curved bearing surfaces for tractive links do not substantially increase the wear characteristics of the links in the manner of the present invention.